I have tried hard to find home automation products that use this technology, but have failed. This would have all the benefits of a wireless system (no extra wiring) without the downsides of wireless signals (plus, two-way communication would be easier).

Don't know of any. The market for automation components is already small. If you couple a product to powerline networking, it further limits it. The wireless systems have already been cost-optimized, I don't think we'll see much movement into powerline...